How do I know if I have pneumonia? I think I might but not sure..?

This past week I havnt been feeling too well.. I cant tell if it's just bad allergies with a cold or what. I've had a pretty bad cough that is followed with a lot of drainage of flemn in my throat. Feels like I don't have as much energy and I've lost some appetite but it seems likes it's coming back. I don't really experience weezing but when I wake up it's kind of hard to breath cause of all the drainage but when I clear it out I can breath fine. I havnt really had a fever but I feel warm at times.. Just don't really know what to do, thanks for the help!